The present invention is directed, in general, to control signal suppression and, more specifically, to a system and method for suppressing in-band stimuli and a telecommunications infrastructure incorporating the system or the method.
When the public switched telephone network (PSTN) was first put in place decades ago, it was analog-based and employed in-band pulse-width modulated (PWM) control signals to control telecommunications equipment connected to the PSTN. Soon thereafter, in-band dual tone multifrequency (DTMF) tones came into use to achieve in-band signaling. Dial tones, busy signals and other inter-equipment control signals were created with DTMF tones.
As the years progressed, the PSTN evolved from analog systems to the digital systems that are now in wide use. In today""s mostly digital PSTN, almost the entire network is digital, except for most of the telephone lines strung between central offices (COs) and customer premises, which remain analog. User traffic transmitted over the analog telephone line is converted to digital information at the COs. Once the digital information reaches the last CO in line, the digital information is converted back to an analog format.
Today""s digital PSTN systems also transmit control signals out-of-band instead of in-band. This prevents a user from hearing any of the control signals while having a conversation. However, telephony line cards and applications still exist that respond to in-band control signals.
Many current computer systems and voice processing applications have the capability to store and transmit user traffic in both digital and analog formats. Problems can occur when speech containing in-band control signals (generated accidentally or intentionally) is transmitted to equipment or systems that respond to in-band control signals. For example, if a message contains concurrent frequencies or silence that a voice mail machine might misinterpret as being in-band control tones, the voice mail machine might fail to deliver the message or modify the message in some undesirable manner.
Accordingly, what is needed in the art is a way to prevent in-band control signals from causing unexpected or unintended results in systems or applications that still recognizes in-band control signals.
To address the above-discussed deficiencies of the prior art, the present invention provides, for use with analog telecommunications equipment that responds to in-band stimuli, a system for, and method of suppressing an in-band stimulus and a telecommunications infrastructure employing the system or the method. In one embodiment, the system includes: (1) a stimulus detector, associated with the analog telecommunications equipment, that detects a presence of the in-band stimulus and (2) a stimulus suppressor, coupled to the stimulus detector, that alters the in-band stimulus to cause the analog telecommunications equipment to disregard the in-band stimulus.
The present invention therefore introduces the broad concept of suppressing, or disabling, stimuli before analog equipment has an opportunity to act on them. A xe2x80x9cstimulusxe2x80x9d is defined for purposes of the present invention as an affirmative control signal, such as one or more tones (including DTMF signals) or a period of subthreshold amplitude variation (a period during which the amplitude of the user traffic varies less than a threshold set by the analog telecommunications equipment such that the equipment interprets the period as a period of silence). An xe2x80x9caffirmative control signalxe2x80x9d can be a command or convey operating status.
In one embodiment of the present invention, the in-band stimulus is a dual tone multifrequency (DTMF) signal and the stimulus suppressor alters the in-band stimulus by altering a tone in the DTMF signal. The stimulus suppressor may attenuate, frequency-shift, truncate, distort or eliminate the tone completely to suppress the DTMF signal as a whole.
In one embodiment of the present invention, the in-band stimulus is a period of subthreshold amplitude variation and the stimulus suppressor increases the amplitude variation during the period. The stimulus suppressor may inject noise into the user traffic or variably amplify the user traffic to increase variation and thereby fool the analog telecommunications equipment into disregarding the period as being a period of silence.
In one embodiment of the present invention, the in-band stimulus is selected from the group consisting of: (1) a dial tone, (2) a busy signal, (3) a ringback signal and (4) an offhook signal. Those skilled in the art will understand, however, that the principles of the present invention are applicable to any type of in-band signaling.
In one embodiment of the present invention, the system is located in the analog telecommunications equipment. In an alternative embodiment of the present invention, the system is located in a conference bridge. The system may alternatively be located in a switch associated with the public switched telephone network (PSTN). The system may, in fact, concurrently exist at many locations.
In one embodiment of the present invention, the system is embodied in a sequence of software instructions. Alternatively, the system of the present invention may be embodied in hardware or firmware, as the particular application may find advantageous.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.